This went to the GJ because simple dismissal would have garnered understandable outrage.
The GJ is there to decide if a viable case exists. This GJ, spending an extraordinary effort to review evidence, concluded there simply was no case.
Yes, a decent prosecutor can persuade a GJ to indict a ham sandwich - but then that same prosecutor would have to prosecute that ham sandwich, which is a stupid career-destroying move.
Prosecutors don’t bring cases they think are so un-viable that a GJ wouldn’t indict, hence the near-100% indictment rate. The few they do bring are either surprises or, like this one, an attempt to get practical certification that it’s not worth pursuing.
Why is outrage understandable?